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Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation

From Boqun Feng <boqun.feng@gmail.com>
Newsgroups linux.kernel
Subject Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation
Date 2017-09-06 02:50 +0200
Message-ID <umwHv-1VB-7@gated-at.bofh.it> (permalink)
References (5 earlier) <umiuS-WJ-21@gated-at.bofh.it> <umjqV-1ux-3@gated-at.bofh.it> <umjKi-1Bt-13@gated-at.bofh.it> <ummoN-3iq-5@gated-at.bofh.it> <umvV7-1o3-3@gated-at.bofh.it>
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On Wed, Sep 06, 2017 at 08:52:35AM +0900, Byungchul Park wrote:
> On Tue, Sep 05, 2017 at 03:46:43PM +0200, Peter Zijlstra wrote:
> > On Tue, Sep 05, 2017 at 07:58:38PM +0900, Byungchul Park wrote:
> > > On Tue, Sep 05, 2017 at 07:31:44PM +0900, Byungchul Park wrote:
> > > > Recursive-read and the hint I proposed(a.k.a. might) should be used for
> > > > their different specific applications. Both meaning and constraints of
> > > > them are totally different.
> > > > 
> > > > Using a right function semantically is more important than making it
> > > > just work, as you know. Wrong?
> > 
> > > Of course, in the following cases, the results are same:
> > > 
> > >    recursive-read(A) -> recursive-read(A), is like nothing, and also
> > >    might(A)          -> might(A)         , is like nothing.
> > > 
> > >    recursive-read(A) -> lock(A), end in a deadlock, and also
> > >    might(A)          -> lock(A), end in a deadlock.
> > 
> > And these are exactly the cases we need.
> > 
> > > Futhermore, recursive-read-might() can be used if needed, since their
> > > semantics are orthogonal so they can be used in mixed forms.
> > > 
> > > I really hope you accept the new semantics... I think current workqueue
> > > code exactly needs the semantics.
> > 
> > I really don't want to introduce this extra state if we don't have to.
> 
> OK. If the workqueue is only user of the weird lockdep annotations, then
> it might be better to defer introducing the extra state until needed.
> 
> But, the 'might' thing I introduced would be necessary if more users
> want to report deadlocks at the time for crosslocks with speculative
> acquisitions like the workqueue does, since the recursive-read thing
> would generate false dependencies much more than we want, while the

What do you mean by "false dependencies"? AFAICT, recursive-read could
have dependencies to the following cross commit, for example:

	A(a)
			ARR(a)
			RRR(a)
	WFC(X)
			C(X)

This is a deadlock, no?

In my upcoming v2 for recursive-read support, I'm going to make this
detectable. But please note as crossrelease doesn't have any selftests
as normal lockdep stuffs, I may miss something subtle.

Regards,
Boqun

> 'might' thing generate them just as many as we want.
>

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Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Peter Zijlstra <peterz@infradead.org> - 2017-08-29 11:10 +0200
  [tip:locking/core] locking/lockdep: Untangle xhlock history  save/restore from task independence tip-bot for Peter Zijlstra <tipbot@zytor.com> - 2017-08-29 16:30 +0200
  Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <max.byungchul.park@gmail.com> - 2017-08-29 18:10 +0200
    Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Peter Zijlstra <peterz@infradead.org> - 2017-08-29 20:50 +0200
  Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <byungchul.park@lge.com> - 2017-08-30 04:20 +0200
    Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <byungchul.park@lge.com> - 2017-08-30 09:50 +0200
      Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Peter Zijlstra <peterz@infradead.org> - 2017-08-30 11:00 +0200
        RE: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation "Byungchul Park" <byungchul.park@lge.com> - 2017-08-30 11:10 +0200
          Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Peter Zijlstra <peterz@infradead.org> - 2017-08-30 11:20 +0200
            RE: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation "Byungchul Park" <byungchul.park@lge.com> - 2017-08-30 11:40 +0200
          Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Peter Zijlstra <peterz@infradead.org> - 2017-08-30 11:20 +0200
            RE: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation "Byungchul Park" <byungchul.park@lge.com> - 2017-08-30 11:30 +0200
              Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <byungchul.park@lge.com> - 2017-08-30 13:30 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <max.byungchul.park@gmail.com> - 2017-08-30 15:00 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <byungchul.park@lge.com> - 2017-08-31 09:30 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Peter Zijlstra <peterz@infradead.org> - 2017-08-31 10:10 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <byungchul.park@lge.com> - 2017-08-31 10:20 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Peter Zijlstra <peterz@infradead.org> - 2017-08-31 10:40 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <byungchul.park@lge.com> - 2017-09-01 04:10 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Peter Zijlstra <peterz@infradead.org> - 2017-09-01 11:50 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <byungchul.park@lge.com> - 2017-09-01 12:20 +0200
                RE: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation 박병철/선임연구원/SW Platform(연)AOT팀(byungchul.park@lge.com)          <byungchul.park@lge.com> - 2017-09-01 14:10 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Peter Zijlstra <peterz@infradead.org> - 2017-09-01 14:40 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <max.byungchul.park@gmail.com> - 2017-09-01 16:00 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Peter Zijlstra <peterz@infradead.org> - 2017-09-01 18:40 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <byungchul.park@lge.com> - 2017-09-04 03:40 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <byungchul.park@lge.com> - 2017-09-04 04:10 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Peter Zijlstra <peterz@infradead.org> - 2017-09-04 13:50 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <byungchul.park@lge.com> - 2017-09-05 02:40 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Peter Zijlstra <peterz@infradead.org> - 2017-09-05 09:10 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Peter Zijlstra <peterz@infradead.org> - 2017-09-05 09:20 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <byungchul.park@lge.com> - 2017-09-05 11:00 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Peter Zijlstra <peterz@infradead.org> - 2017-09-05 11:40 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <byungchul.park@lge.com> - 2017-09-05 12:40 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <byungchul.park@lge.com> - 2017-09-05 13:00 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Peter Zijlstra <peterz@infradead.org> - 2017-09-05 15:50 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <byungchul.park@lge.com> - 2017-09-06 02:00 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Boqun Feng <boqun.feng@gmail.com> - 2017-09-06 02:50 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <byungchul.park@lge.com> - 2017-09-06 03:40 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <byungchul.park@lge.com> - 2017-09-07 02:00 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <byungchul.park@lge.com> - 2017-09-07 02:20 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <byungchul.park@lge.com> - 2017-09-06 02:50 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Peter Zijlstra <peterz@infradead.org> - 2017-09-05 13:00 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <byungchul.park@lge.com> - 2017-09-05 13:30 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <byungchul.park@lge.com> - 2017-09-05 10:40 +0200
              Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Peter Zijlstra <peterz@infradead.org> - 2017-08-31 10:10 +0200

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